The problem of the increasing speed idle and the hunting idle should be fixed by this procedure. I have read many posts on the VW newsgroup and read many letters to the Corrado mailing list that describes this problem.
Disclaimer: This is a suggested fix for a common G60 problem. By no means is this guaranteed to fix your problem. I claim no responsibility for mistakes made or other problems created. Please read this entire article before to determine if this is what your car is doing and understand what you are doing.
Scenario: You put in a new chip just recently or some time ago. Now when the temp outside gets above 60 degrees F the idle stays at 1100rpms. When you put on the AC the idle hunts between 700 and 1400 rpms. You have replaced the coolant temp sensor, o2 sensor , checked timing, cleaned the isv and basically banged your head against a wall for way too long on this problem. If this sounds like your car read on.
Problem: When you put in your chip you removed the ecu from the car and from its mounting bracket, you put your greasy fingers all over the bracket and the ecu. Also, you broke the original contact space the ecu had with the bracket. This is causing a bad ground and low voltage to the ecu.
Solution: Take the ecu back out of the car. Take some 200 wet sandpaper or a file or a wire brush/wheel or a scotch bright pad and clean the spots where the ecu contacts the bracket. Also, clean the ecu side where it contacts the mounting bracket. What you want is a nice shiny metal on metal contact. Then clean where the bolt on the body contacts the mounting bracket. Now, when you put the ecu back in the car don't be afraid to really tighten down the ecu mounting bolt. Don't snap it off, but put it down to 15-20 ft/lbs.
You car should now start up on the first crank, idle at 800 rpms, and overall run better. If this did not correct your problem check the condition of the vacuum line to the ecu and the grounds at the throttle body. If you have gotten through all this and the car still idles bad then you are stuck in open loop for some reason. Check thermostat, o2 sensor ground, and all other sensor outputs. Hopefully though you love you Corrado again.
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